17 

falls into and is directly continuous with its fellow of the opposite side, 
the two arteries thus forming what has the appearance of being a 
delicate cross-commissural vessel connecting the much larger vessels 
formed, on either side, by the continuous common and external carotid 
arteries. At the middle point of the commissure there is a small tit-like 
eminence which must representapersisting remnantof a median encephalic 
prolongation of the internal carotids such as is found in elasmobranchs. 
And it is to be particularly noted that the internal carotid of Chimaera 
does not abort throughout its entire length anterior to this point, the 
only portion that aborts being that short section of the artery that 
must have extended, in younger stages, from the point where it 
anastomosed with its fellow of the opposite side to the point where 
it received the dorsal end of the efferent mandibular artery. Beyond 
the latter point, the artery certainly still persists in the adult, and 
appears as the cerebral prolongation of the so-called anterior carotid. 
The external carotid, after its separation from the internal carotid, 
turns laterally, in a short curve, and then, turning dorsally, perforates 
the cartilaginous floor of the orbit near its lateral edge. Having 
entered the orbit it immediately separates into two branches one of 
which turns anteriorly and the other posteriorly. The posterior branch 
curves dorsally and then forward, above the nervus opticus, and 
having supplied all the muscles of the eye-ball sends terminal branches 
to accompany the ophthalmicus nerves, and to supply the latero- 
sensory canals. The anterior branch runs forward ventral to the 
nervus opticus and separates into two parts, one of which goes toward 
the snout while the other goes toward the mandible; these two 
branches forming anastomoses with each other and supplying the 
muscles and tissues of the region. 
The arteries as here described and homologized are diagramma- 
tically shown in the accompanying Fig. 2, that short portion of the 
internal carotid that has aborted being indicated by a dotted line. 
From this diagram it is seen that what I have defined (ALLIS, 1908) 
as the mandibulo-internal type of internal carotid is absolute in 
Chimaera, and this is apparently a definite characteristic of the 
Holocephali. 
Palais de Carnolés, Menton. June 5th, 1912. 
(Eingegangen am 29. Juni.) 
Anat. Anz. Bd. 42. Aufsätze, 2 
